Man, it amazes me how just a short distance can lead to so different weather. We've actually had to lay irrigation hose under our mulch to ensure young crops are getting enough water when normally we'd be worried about the soil becoming waterlogged at this time of year. Hope your crops pull through Paradoxbox.

I've moved out of the mountains though I'm maintaining the property indefinitely. Some crops were failures, demanding plants like tomatoes look like they'll be a bust, but undemanding stuff is growing well. Herbs, lettuce, etc. doing well. Boatloads of cilantro/pakuchi. The proximity to the mountains probably has a lot to do with it but the sheer amount of cloud cover and rain seems a little abnormal, I'm guessing this year and last have just been bad weather years in this region.

There are very few tomato varieties that seem to do well outside in Japan, the only ones we've found that will grow well outside of a poly tunnel are San Marzano that don't seem bothered but hot humid conditions. Any other varieties just turn to mush within a short space of time.

Have to say that this year it is one of the dryest rainy seasons I've experienced since coming to Japan. Many of the rice farmers I follow on Instagram are having real problems with the lack of rain and some may actually be in danger of loosing their entire crops if they don't get some heavy rain soon. Couple that with the low harvests many were able to crop last year due to the lack of sun and we might see prices for rice go up again this year.

My costoluto varieties did alright a few years ago and last season I got a few as well, but the rain was the real problem. I think the tomatoes can handle the humidity as long as they're getting enough wind to stop rot and sunlight, but with constant cloud and rain they just turn to mush.

I might try creating a sort of wind funnel by planting fast growing vegetation on the open area of the property and see if that can push some wind towards the plants, but if the cloud cover is like this every year it probably won't help much. Might be time to look for some crops that can handle being constantly drenched. The property dips well below average temps for Kanto at night though, even this week it's dipped below 15c at 5am. Might need to look at specific mountain jungle crops to be able to grow well here.

We also found some European tomato varieties able to survive the rainy season, albeit with a hefty amount of leaf loss but then bounce back after the rains have slackened off. San Marzano and Roma being the two strongest we found but last year neither of them were able to thrive and as the rainy season didn't stop they died out in August.

You could try growing sorghum (ソルゴー) to channel the wind, it loves rainy season type weather and grows pretty tall, a massive bag of seeds that will last you several years is relatively inexpensive and it makes an excellent cover crop/green manure plus it's roots clear the ground of nematodes.

Sasage (yard long beans) positively thrive during the rainy season and Thai basil just shrugs the rain off when other basils are turned to mush and obviously nasu do well.